1. Field of the Invention
This invention relates generally to screening decks for screening particulate material and particularly to an apparatus and method for mounting modular screens on a screening deck without altering the deck structure.
2. Background of the Invention
Crowned screening decks are prevalent in industries segregating particulate matter, e.g., gravel, by size. The screen is typically a lattice of resilient, high strength, wear resistant wire providing a selected screen aperture size. The screen extends across the full width of the deck. Longitudinal support beams of uneven height support the screen and define a radius of curvature for the crown. The screen, which has formed hooks or the like along each side, is tensioned and forced to conform to the crown by attachment at longitudinal side clamps of the deck. This assures that the screen bears tightly against the support beams to maintain the crown and to minimize wear between the beams and the screen.
The screen does not always wear uniformly. An entire screen is replaced even for excess wear only in a small area or for localized damage during use. The screen itself is expensive and the changeover is tedious and time consuming. The longitudinal side clamps, which have multiple bolt fasteners, must be removed before the screen can be removed and replaced. To avoid the cost and down-time associated with replacing an entire screen, screening decks often employ modular screen components. Thus, a large screen is replaced with multiple small screens or modules covering the entire screening deck, but which may be individually replaced upon the occurrence of localized wear or damage. Generally, such modular screen systems have been applied to flat screening decks, i.e., a screening deck with support beams of even height defining a flat screen area as opposed to a crowned screening area.
A plank type screening system disclosed by Trelleborg in International Publication No. W083/02075 as published Jun. 23, 1983 under the Patent Cooperation Treaty. The screens of the Trelleborg system must extend the full width of the screening deck and clamp down at the side clamps of the deck in a manner similar to that of the full width crowned screen. The clamps must be removed from the sides of the deck when removing and replacing a screen. The clamps, however, typically hold several screens and the release of one pair of side clamps releases all screens held by those clamps. Thus, in replacing a single screen of the Trelleborg system several screens are necessarily unclamped, and may require repositioning in reassembly of the system.
Small individual screen modules, i.e., less than the full width of the screening deck, have been utilized- The individual screen modules cannot mount to the crowned deck in the same manner as that of the full width crowned screen or that of the plank type module. The support structure of the crowned deck, therefore, must be replaced or altered in order to accept the smaller screen modules. Generally, such modification converts the crowned screening deck to a flat screening deck. In other words, the longitudinal support beams are converted to or replaced with support beams of even height. Also, lateral support beams are, in some cases, are added between the longitudinal support beams to complete a matrix-like support structure for receiving screen modules. The new beams have mounting holes for receiving fasteners for holding individual screen modules. Screening decks rarely have width dimensions matching an even multiple of the screen module width. Accordingly, in converting a crowned screening deck into a screening deck for receiving screen modules, the conversion must include fortification along the side walls and extending toward the center of the screening deck to fill in the side gaps therealong left by a matrix of screen modules not filling the entire screening deck width. While the deck alteration provides the capability of accepting modular screens, such alteration may void the manufacturer's warranty. In addition, the altered deck is no longer a crowned screening deck and is no longer useable with the full width tensionable screens.
Various fasteners have been developed to attach the screen modules to the support beams. Most of the fasteners are separate from the screen modules and are easily damaged, dropped, misplaced or lost in the process of screen changeover. Generally, such fasteners have been point-to-point attachments, e.g., as by engaging the screen module by mounting pins or plugs at the screen module corners and provide no freedom of mounting position. U.S. Pat. No. 4,661,245 issued Apr. 28, 1987 to Rutherford et al shows a modular screen assembly with downward protruding formations coupling to corresponding formations of the underlying screen deck.